GFP-tags have been extremely useful in the genetic dissection of molecular pathways that regulate the formation of synapses in model organisms such as C. elegans. Similarly, many such fusion proteins are now being used to examine synaptic development in cultured mammalian neurons. However, such fusions remain largely unutilized in Zebrafish even though the fish is uniquely suited for forward genetic dissection of synaptic development because of its fast development, transparent body during larval development, and the ease of genetic manipulation. With the genome sequence of Zebrafish nearing completion, such tools are ripe for development in the Zebrafish. As a first step in developing a research program in Zebrafish aimed at dissecting the molecular mechanisms that regulate the specificity of synapse target selection, I propose to create a set of GFP-tagged synaptic proteins to facilitate the analysis of synapse formation in vivo in Zebrafish embryos and larvae. Using a combination of modern recombinant DNA technologies (the GAL4/ DAS system, Gateway cloning technology, transposon vectors, and bacterial artificial chromosomes), I propose to create vectors for expression of Zebrafish synaptic protein-GFP fusions and transgenic Zebrafish animals expressing these synaptic protein-GFP constructs. We will concentrate on 'moving' constructs that we have shown in C. elegans to express robustly and precisely and label either synaptic vesicle populations or the active zone domain of the synapse. Specifically, we have recently created a novel fusion to a C. elegans synaptic vesicle protein that allows for 10-fold more sensitive detection of synapses in live worms. Furthermore, this C. elegans fusion works across species as the worm protein fusion localizes robustly to the neuromuscular junction when expressed in Drosophila. Preliminary studies indicate that the equivalent Zebrafish fusion forms puncta when expressed in neurons in a transient expression system suggesting it localizes to synapses. We propose to develop this fusion in Zebrafish to label presynaptic specializations. Similarly, we propose to test whether several recently developed C. elegans active zone tags will permit the visualization of Zebrafish active zones when the analogous Zebrafish protein fusions are expressed in Zebrafish neurons. [unreadable] [unreadable]